1. Technical Field of the Invention
The present invention relates generally to a copyright information embedding apparatus designed to embedding information for managing copyright in a storage medium when recording analog signals such as audio signals in digital form, and a record carrier recording thereon that information.
2. Background of Related Art
Optically readable discs such as "Compact Discs" have come into wider use as audio record carriers than conventional magnetic tapes. An EFM recording format using 8-bit fixed length data symbols and a data format including a subcode, audio data, and a CRC are established as logical formats for CDs. CD players having a variety of application functions are being developed.
CDs are also used as CD-ROMs by discriminating control bits (four bits) in a subcode of a Q channel or detecting the absence of a TOC and have wide applicability to the field of electronic publication for mass storage and high-speed access. The CD-ROMs, however, have the drawback in that audio signals are compressed by ADPCM, which makes it impossible to reproduce the audio signals at original quality levels. A recording system designed to achieve the high fidelity is sought. In other words, development of optical discs capable of recording audio signals within a band of twice that of a conventional CD is expected.
Such high-quality hi-fi signals do not deteriorate in a duplication process as long as they are copied in digital form, which is quite convenient for users, but undesirable from the viewpoint of copyright protection. For avoiding such a problem, a system designed to limit the number of copies of digital information (U.S. Pat. No. 5,428,598), a system having no digital signal output terminals, a system designed to remove part of a band of an analog output signal, a system embedding copyright data into digital data (U.S. Pat. No. 5,319,735), and a system identifying an user who made a copy by detecting an identification signal formed by slightly changing original data, have been proposed.
The system embedding copyright data into digital data, however, has the drawback in that D/A conversion of the digital data into analog audio signals in a reproduction operation would cause reproduced sound quality to be deteriorated or changed uncomfortably.